1. Field of the Invention
This invention relates to an improved process for preparing quaternary ammonium salts and more particularly this invention relates to a continuous process for preparing quaternary ammonium chlorides by reacting a tertiary amine with an organic chloride in the presence of a heterogeneous catalyst.
2. Related Art
The preparation of quaternary ammonium salts is known in the art. A good overview of the production of cationic surfactants from fatty nitriles is found in an article titled "Industrial Production of Fatty Amines and Their Derivatives",JAOCS, 61, No. 2(Feb. 1984). It is noted that the largest volume and most important class of quaternary ammonium salts is difattydimethyl ammonium salts, produced from secondary amines with methyl chloride under continuous addition of alkali.
In addition, known methods of preparation of quaternary ammonium compounds are discussed at p.526 in Encycl. Chem. Techn. 3rd Ed.(Hoechst) 19:521(1982). Generally a suitable tertiary amine is reacted with an alkylating agent, such as an alkyl ester. There are many variations in the final product because of the large number of diverse starting amines and alkylating agents. The tertiary amines used commercially are derived from synthetic or natural raw materials.
In U.S. Pat. No. 3,175,008 there is disclosed a method for preparing tetraaliphatic ammonium chloride by mixing an aliphatic secondary amine, sodium bicarbonate and alkyl alcohol having from 1 to 4 carbon atoms with methyl chloride at a temperature of at least 60.degree.-70.degree. C.
In U.S. Pat. No. 3,377,382 there are disclosed novel fatty quaternary ammonium compounds containing residual fatty acid monomers left after the polymerization of higher unsaturated fatty acids having about the same properties as dimethyl dihydrogenated tallow alkyl quaternaries which are commonly used for their softening properties.
In the processes discussed above the methods of production are not continuous. The discontinuous type reaction is less efficient because much more time is required to fill, heat and vent the reaction vessel. Also more of the alkyl chloride is lost as a result of repeated venting of the reaction vessel.
A continuous process for the manufacture of quaternary ammonium chlorides containing at least one aliphatic group of 8 to 22 carbons is disclosed in U S. Pat. No. 3,813,441 where amines are reacted with methyl chloride in the presence of an alkali metal hydroxide. In that invention the reaction is carried out in the presence of corresponding quaternary ammonium compounds which decreased saponification of methyl chloride. Further, the use of alkali hydroxides in place of sodium bicarbonate considerably improved the color of the quaternary ammonium compounds. The disadvantages of that process include corrosion caused by using caustic and also the need to dispose of a large amount of by-products.
It would be a distinct advance in the art if quaternary ammonium salts were continuously produced over a heterogeneous catalyst. If such a process offered high turnover rate, and high selectivity, such a process would fulfill a need in the art.